text: 
  
  var my_array = [4, 34, 1, 23, 990, 23, 2]
  
  for (i=0; i<my_array.length; i++) {
  	my_array[i] = my_array[i]*2;
  }
  
  console.log(my_array)
  
  // -------------------------------
  
  var my_array = [4, 34, 1, 23, 990, 23, 2]
  
  for (num in my_array) {
  	my_array[num] = my_array[num]*2;
  }
  
  console.log(my_array)